The present invention relates generally to mechanical actuation systems for driving aircraft secondary flight control surfaces, and, more particularly, to an improved torque limiter, sensitive to differential output torque, that is particularly adapted to be used in such actuation systems.
Aircraft flight control surfaces are frequently driven by mechanical actuation systems. This method of control has been found to be efficient in terms of space and weight, and can inherently provide synchronization of airfoil surfaces. These mechanical systems generally incorporate torque limiters so that a jam at one point does not necessarily result in damage to other parts of the system.
In a typical installation, the system comprises a central power drive unit (xe2x80x9cPDUxe2x80x9d), which converts hydraulic or electrical power into mechanical power in the form of torque and rotational speed. The PDU will typically have two mechanical outputs, one for each wing, and each output will be protected with a torque limiter. The torque limiter is set to limit torque to a maximum value, which is typically equal to the total torque required for normal operation by the components in one wing, plus a margin of, say, thirty percent, to account for aircraft and flight condition variability and assembly tolerances. If this torque limit is exceeded, the limiter will lock the PDU input to ground, and all system motion will cease.
The system may drive two or more mechanical actuators in each wing. If one actuator jams, it will be subjected to the full torque limit setting that may be in excess of twice its normal operating load. All of the components of the system must be designed for this large load to prevent secondary damage.
With parenthetical reference to the corresponding parts, portions and surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention broadly provides an improvement in a differential coupling (20) having a body (21), having a rotary input member (22), and having two rotary output members (23, 24), the algebraic sum of the angular displacements of said output members being proportional to the angular displacement of said input member, the improvement comprising: a detent mechanism (31, 45, 34) operatively arranged to prevent relative angular displacement between said output members whenever the difference between the torques acting on said output members is less than a first predetermined value, and to allow relative angular displacement between said output members whenever the difference between the torques acting on said output members is greater than said first predetermined value; a brake (38) mounted on said body and operatively arranged to be selectively applied to brake rotation of said input member; and a differential mechanism (43) having a mechanical output (44) proportional to the relative angular displacement between said output members, and operatively arranged to cause said mechanical output to energize said brake.
The relative angular displacement between said output members may be less than a second predetermined value. The detent mechanism may be arranged to constrain said mechanical output. The differential mechanism may be operatively arranged to apply said brake in proportion to the relative angular displacement between said output members. The differential mechanism may includes a planetary gear (43) rotatable about an axis and operatively engaging said output members, and wherein said differential mechanism is arranged to operate said brake as a function of the rotation of said planetary gear about said axis. The mechanical output may be a pin (44) located at an eccentric position on said planetary gear, and may further comprise a preloaded spring operatively engaging said pin to establish said first predetermined value.
Accordingly, the general object of the invention is to provide an improved coupling.
Another object is to provide an improved torque limiter, sensitive to differential output torque.
Another object is to provide protection against secondary system damage, due to downstream jams and disconnects, at a lower system weight than allowed by the prior art.
Still another object is to provide an improved coupling in which differential motion between two outputs is limited to a predetermined value.
These and other objects and advantages will become apparent from the foregoing and ongoing written specification the drawings, and the appended claims.